1. Technical Field
The present invention relates to a method of assembling an inflator for a vehicle occupant restraint, such as an air bag.
2. Description of the Prior Art
The use of an air bag to restrain movement of an occupant of a vehicle when the vehicle encounters a sudden deceleration, such as in a collision, is well known. The air bag is inflated by gas generated by activation of gas generating material. The gas generating material is contained in an inflator housing.
A commonly used gas generating material contains an alkali metal azide and a metal oxide, such as cupric oxide or iron oxide. Ignition of the gas generating material produces a hot gas stream. The hot gas stream will typically include nitrogen gas, molten metal, sodium oxide, a sodium salt of the metal, and metal nitride. The nitrogen gas carries the other reaction products which are in the form of a residue or sinter.
A problem facing the air bag industry has been the development of an effective, low cost, mechanical filter for filtering the residue and the sinter from the hot gas stream. The filter must be capable of removing the residue and the sinter from the gas before it enters the bag. The filter also should be capable of cooling the gas stream. A portion of the filter may have a reactant surface of an acidic oxide, such as silicon dioxide, to react with and neutralize the sodium oxide in the hot gas stream. To achieve these objectives, a seal must be provided between the filter and the inflator housing, so that all of the hot gas stream is directed through the filter.
U.S. Pat. No. 4,902,036, discloses an inflator or gas generator for a vehicle occupant restraint. The inflator contains a plurality of filters including a final filter assembly which cools and filters the gas before the gas exits from the generator into an air bag. The final filter assembly comprises a first section of mesh screens. The mesh screens remove particulate reaction products from the gas stream. The final filter assembly also has a second section of mesh screens of smaller mesh size than the first section of mesh screens. The mesh screen sections are separated from each other by a spacer pad of a ceramic fiber that is a mixture of aluminum oxide and silicon dioxide. The spacer pad is sold under the trademark "Fiberfrax" by Sohio Carborundum, Inc. It is also known to have the foregoing final filter assembly seal against the generator housing by pressing graphite seals (not shown in the patent) between the housing and the upper and lower edges of the filter.
U.S. Pat. No. 4,878,690 also discloses a filter assembly used in an inflator for a vehicle occupant restraint. The filter assembly comprises, in the direction of gas flow, a plurality of layers of 28 mesh stainless steel screen, a filter member for fine filtering the generated gas, and then another layer of 28 mesh stainless steel screen. The filter member can be an alumina-silica fiber paper such as "Lytherm" ceramic fiber paper marketed by Mansville Co. Other examples of filter paper disclosed in the patent are silica fiber paper marketed by Sandtex Corporation of Japan under the trademark "Sandtex" and a filter material sold by National Standard Co. of Corbin, Ken. under the trademark "FIBREX". There is no disclosure in the patent as to how the filter assembly is sealed against the housing for the inflator.